Microbial populations and their relationships

microbial populations and their relationships:
dr. jawad kadhum tarrad
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types and general properties of microorganisms :

1. bacteria:
1. the bacteria are prokaryotic cell which has not true nucleus but has single circular loosely chromosome in cytoplasm lacking nuclear membrane.
2. the bacteria are unicellular, they contain no organelles except small 70s ribosome .
3. most bacteria have rigid cell wall that contain peptidoglycan , some may have flexible or lack cell wall.
4. the bacteria replicate by binary fission. during which one parent cell divided to make two progeny cells.
5. most bacteria have not locomotion organelle ,but some bacteria are motile.
6. some bacteria form endospore to survival in adverse conditions.
2. viruses:
viruses are unlike any other forms of organisms. they are different from other infectious organisms in the following specific properties:
1. viruses possession of only one type of nucleic acid , either dna or rna , but never both.
2. viruses are not considered as cell because they lack cellular organelles such as: nucleus, cytoplasm, mitochondria, ribosome, golgi apparatus, and endoplasmic reticulum.
3. viruses replicate only within living host cell , they are not capable of independent replication. therefore they are known as obligate intracellular particles, because lack necessary enzymes for synthesis of proteins and nucleic acid, so entirely dependent up on host cell energy for synthesis of macromolecules.
4. viruses replicate by complex process. they can not replicate by binary fission or mitosis . the viruses produce many copies of their nucleic acid and proteins, and then reassemble into multiple progeny viruses. one virus can replicate to produce hundreds of progeny viruses , whereas other organisms , one cell divides to produce only two daughter cells.
5. all viruses are pathogenic, and the viruses infect all types of organisms in nature( such as animals, plants, fungi, bacteria).
6. viruses can not seen by light microscope but by electronic microscope.
7. they are unaffected by antibiotic agents but sensitive to antiviral chemotherapy agents and interferon .
3. fungi :
1. fungi are eukaryotic and more complex than bacterial cell (have a true nucleus and other cellular organelles) .
2. fungi either unicellular(yeasts) or multicellular(molds) organisms, unlike prokaryotic organisms .
3. fungi are not photosynthetic and have no chlorophyll pigment (therefore, fungi non-autotrophic but heterotrophic ).
4. most fungi are obligate aerobes, some are facultative anaerobe, but none are obligate anaerobes.
5. natural habitat of most fungi is soil environment , except some yeasts such as : candida and malassezia are part of human normal flora.
6. most fungi normally live saprophytic in the nature. but some genera are pathogenic for human , animal and plants.
7. fungi have no organelles for locomotion (fungi non-motile).
8. reproduction of fungi occurring sexually and asexually spores, whereas ,bacterial spores are formed in unsuitable conditions for survival , not for reproduction .
4. parasites:
1. parasites are eukaryotic , and more complex having cellular organelles.
2. parasites either unicellular (protozoa) or multicellular(metazoan) organisms.
3. parasites are reproduced by sexual(conjugation) or asexual (binary fission ).
4. most parasites are motile by either cilia or flagella or pseudopodia.
5. natural habitat of most parasites is soil environment , some in water or on plants . some parasites are part of human normal flora.
5. algae:
1. algae are group of eucaryotic organisms.
2. algae range from single cell (unicellular)organisms to complex multicellular organisms.
3. algae contain membrane-bound chloroplasts containing chlorophylls ( photosynthetic). they are produce different pigments in their environments.
4. algae inhabit a wide range of habitats from aquatic environments to soil environments.
5. generally, most algae are free-living, some algae have symbiotic relationship with fungi (lichens), mollusks, corals and plants, and some algae can be parasitic.
6. algae can reproduce sexually and asexually.

evolution and classification of microbes:
dating meteorites through the use of radioisotopes places our planet at an estimated 4.5 to 4.6 billion years old. however , conditions on earth for the first hundred million years or so were far too harsh to sustain any type of life .
earth and its solar system formed by physical and chemical processes about 4.5ga ago. microbial fossils were first reported recently 1950s. oldest microbial fossils are found in stromatolites dated at about 3.5 ga old. stromatolites are laminated sedimentary rocks ,some of which were produced by microorganisms. intertidal mat communities are most common type of living stromatolites currently found on earth. this important discovery provided the first convincing evidence that earliest life forms on the earth were microorganisms.
the first direct evidence of cellular life was discovered in 1977 in a geologic formation in south africa known as swartkoppie chert, a granular type of silica. these microbial fossils as well as those from the archaean apex chert of australian have been dated at about 3.5 billion years old. despite these findings, the microbial fossil record is understandably sparse. thus to piece together the very early events that led to origin of life, biologists must rely primarily on indirect evidence. each piece of evidence must fit together like a jigsaw puzzle for a coherent picture to emerge.
the root (ancestor), or origin of life , is placed early in line of descent. evolutionary timeline showing the approximate appearance of life on the earth from 4.5 billion years ago to the present time.







• all types of cells can be divided into two different types according to nature of nucleus: prokaryote and eukaryote . the differences between them are
1. the eukaryotic cell has a true nucleus with multiple chromosomes surrounded by a nuclear membrane . the prokaryotic cell has not true nucleus but has single circular loosely chromosome in cytoplasm lacking nuclear membrane.
2. all types of cells contain both types of nucleic acid(dna and rna) , except viruses contain one type of nucleic acid ,either dna or rna.
3. the prokaryotic organisms are unicellular, whereas eukaryotic either unicellular or multicellular.
4. eukaryotic cells contain cellular organelles (such as mitochondria , lysosome, large 80s ribosome , golgi apparatus and others ), whereas prokaryotic cells contain no organelles except small 70s ribosome .
5. most prokaryotes have rigid cell wall that contain peptidoglycan , whereas eukaryotes not contain peptidoglycan but have flexible cell membrane , except fungi have rigid cell wall with chitin.
6. the prokaryotic cell (eg bacteria) replicate by binary fission , whereas most eukaryotic cells replicate by mitosis . during which one parent cell divided to make two progeny cells. in contrast , viruses produce many copies of nucleic acid and protein , then reassemble into multiple progeny viruses.
7. most protozoa and some bacteria are motile , whereas fungi and viruses are non motile.

• the comparison of medical important organisms.
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characteristic viruses bacteria fungi protozoa
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cells no yes yes yes
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diameter (µm) 0.02-0.3 1-5 3-10(yeasts) 15-25 (trophozoites)
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nucleic acid either dna or rna both both both
type of nucleus none prokaryotic eukaryotic eukaryotic
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mitochondria absent absent present present
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ribosome absent 70s 80s 80s
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nature of capsid and rigid wall contain rigid wall flexible
outer surface lipoprotein envelope peptidoglycan with chitin membrane
proteins
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motility none some none most
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method not binary binary fission budding or mitosis
of replication fission mitosis



• in 1960s, first classification system of organisms is suggest by robert whittaker(1969), all types of organisms (microorganisms and macroorganisms) classified into five kingdoms: monera(more than 100,000 species) ,protista(60,000 species) , fungi(100,000 species) , plantae(720,000 species) and animalia(1000,000 species) .
this classification scheme of organisms based on at least three major criteria:
1. cell type: prokaryotic or eukaryotic.
2. level of cellular organization: unicellular or multicellular.
3. nutritional type: autotrophic or heterotrophic.

the bacteria belong to monera kingdom. protozoa are members of protista kingdom. the fungi belong to fungi kingdom ,and the helminthes are classified in animalia kingdom.
the viruses are quite distinct from other organisms , they are not cells but particles.
there are five kingdoms of living things.
kingdom type of cell organism
monera prokaryocyte bacteria
actinomycetes
protista eukaryocyte protozoa
fungi eukaryocyte fungi
plantae eukaryocyte plants, moss
animalia eukaryocyte arthropods
mammals
man



the above classification is no longer accepted by most microbiologists. cavalier-smith divides all organisms into two empires and eight kingdoms .
first empire(bacteria)-contain 2 kingdoms(monera divided into eubacteria and archaeobacteria).
second empire(eucaryota)-contain 6 kingdoms ( archezoa, chromista, protista, fungi, plantae, animaliae).

in 1970s , studies by carl woes (1977)based on analysis of 16s rrna suggested the organisms should be divided into three domains (kingdoms):
1. archaea.
2. bacteria.
3. eucarya.
this scheme has widely accepted among microbiologists.
archaea are simple and oldest form of life. many archaea are found in extreme environment, leading to term extremophiles. they are non pathogenic and lack peptidoglycan in their cell wall.
the evolutionary relationships among the three domains of life are represented in universal phylogenetic tree.








microbial relationships:
in addition to, physical and chemical influences , another influences come from other organisms ,the relationships among organisms. these associations may be benefit (positive) or harmful (negative).
• the relationship occurs between two or more dissimilar micro-organisms that are adapted to living together.
• the relationship may be occurred among microbe populations.
• the relationship between microbes and higher organisms such as plants and animals.

to determine the role of microbes associated with a host, normal microbial flora as excellent example of microbial interaction (microbe-host interaction). development of a life-long symbiotic relationship with microbes begins during birth. gnotobiotic animal is possible to deliver an animal by cesarean section and raise that animal in absence of microorganism, that is ,germfree. these microbe-free animals provide suitable experimental models for investigating the interactions of animals and their microorganisms.
louis pasteur first suggested that animals could not live in absence of microorganisms. germ-free animals are usually more susceptible to pathogens, but most completely resistance to intestinal protozoa, entamoeba histolytica, that cause amebic dysentery. this resistance result from absence of bacteria that e.hsitolytica uses as a food source.

types of the relationships:
1. symbiosis which means living together of two dissimilar organisms in same habitat. it is classified as of one of three forms of interactions ( commensalism, mutualism and parasitism) depending on the benefits it provides the symbionts. symbiosis term can used to describe many of interactions between microorganisms and also with higher organisms .
2. non-symbiosis these relationships among organisms include synergism and antagonism.
• synergism : interrelationship between two or more free-living organisms that benefits them. but is not necessary for their survival.
• antagonism: is association between free-living species, in this, some members are inhibited or destroyed by others. these associations such as competition and amensalism. one microbe secrets substances into surrounding environment that inhibit or destroy another member in same habitat.


generally, the relationships are classified into the following kinds:
4. mutualism a symbiotic association in which two different organisms are obligatory dependent upon each other. when separated, in many cases, the individual organisms will not survive. both members benefit from the association.
3. commensalisms(eating at same table): is the association between two organisms in which one partner (commensal , symbiont ) is benefit and other (host)is neither benefit nor harmed.
4. parasitism the organism that lives on or within other organism is benefit and at expense of another organism. the relationship between two organisms ,one organism is benefit from other, and another(host) is usually harmed.
5. synergism(cooperation) in which the growth of one organism either depends on or is improved by growth factors ,nutrients or substances provided by another organisms growing nearby. the organisms exhibiting this interaction are not intimately associated with one another, but benefit from one another (feeding together, both are benefit). for example , decomposes are not only used the decay matters which produce by them, but other genera can used these materials. cooperative relationship is not obligatory , both organisms are benefit. this type of symbiosis involve syntrophic relationship.
6. competition interaction between organisms resulting from a demand for nutrient and energy that exceeds the immediate supply in habitat. one of two competing organisms can dominate the environment, whether by occupying the physical habitat or by consuming a limiting nutrient, it will outgrow the other organism. this clarifies competitive exclusive principle.
7. amensalism : describes the adverse effect that one organism has on another one. a classic example is production of antibiotic that inhibit or kill a susceptible microorganism.
8. predation relationship between two forms of life .the first species (predator) that attacks and kills the second organism (prey).







quorum sensing (qs):

qs : cell to cell communication and work as group within the microbial populations in ecosystem.
the environment that bacteria inhabit are complex and subject to change. in order to successful, bacteria must be able to sense changes in their environment and respond rapidly to these changes by altering the expression of specific genes and metabolic pathways. it is becoming increasingly apparent that most bacteria also produce signals that allow communication between cells. fundamentally, cells communicate by emitting specific chemicals, known as cell-to-cell signals, into a particular environment inhaled by other organisms. when, or if, the concentration of signal reaches a critical threshold , other cell recognize the signal and gene expression of all organisms present may become modified.
communication appears to be important for coordination gene expression within a single population of bacteria (intra-species communication) , between bacteria populations(inter-species communication), and between bacteria and other organisms (inter-kingdom communication). in other word, the communication occurs between related and unrelated bacterial populations ,as between bacteria and their eukaryotic hosts.
the microbes communicate with one another in density-dependent way and carry out a particular activity only when a certain population density is reached. qs refers to minimum number of members in an organization or control of gene expression in response to cell density to regulate a variety of physiological functions .
the increasing cell numbers result in increased signal concentration, resulting in interaction and microbial communication, and group behavior (tiny team work).
the bacteria produce a small substances, which act as chemical signals, these diffusible across cell membrane and they lead to autoinduction in regulatory nature , therefore called autoinducers.
cell to cell communication among prokaryotes occurs by the exchange of small molecules often termed signals or signaling molecules. the exchange of signaling molecules is essential in coordination of gene expression in microbial populations. this first recognized in marine bioluminescent bacterium, vibrio fisheri, which produce light only if the cell are at high density. it has since been discovered that intracellular communication plays an essential role in regulation of genes whose products are needed for the establishment of virulence, symbiosis, biofilm production, plasmid transfer and morphological differentiation in a wide range of microorganisms.

communication signals consist of a wide variety of chemical structures. the primary requirement for cell to cell signals are that they are small, they can be released from cells either by passive diffusion or by active transport, and that other cells recognize them and alter behavioral pattern in response to their presence. because these signals are known to alter bacterial behaviors ,they have been referred to as bacterial pheromones.

some of many possible ecological roles of qs include the following:
a. coordination of gene expression within a single bacterial population.
b. coordination of gene expression and bacterial behavior among multiple population.
c. avoidance of host defense response.
d. direct communication between bacterium and host organism.








gene transfer by¬ sex-pheromone system in enterococcus faecalis



many different gram-negative bacteria produce signal molecules such as: acyl-homoserine lactone (ahl)signal vibrio fisheri, burkholderia cepacia, pseudomonas aeruginosa, use ahl to regulate the expression of virulence factors. wherase agrobacterium tumefaciens will not infect plant and cause gall, erwinia carotorvora will not produce antibiotic without ahl signaling.
gram-positive bacteria usually exchange short peptides called oligopeptides instead to autoinducer-like molecules.enterococcus faecalis ,whose oligopeptide signal is used to determine the best time to conjugate(transfer gene). oligopeptide communication by staphylococcus aureus and bacillus subtilis is used to trigger the uptake of dna from environment.
in gram-positive bacteria, another cell-cell signaling is termed probiotics. probiotics are intestinal bacteria that exert positive effects on the health of human or animal host by interfering with ability of deletingrious bacteria to colonize. probiotic bacteria inhibit colonization via the production of extracellular peptides known as bacteriocins.